1. Field of the Invention
This invention relates to the production of three-dimensional images for television.
2. Description of the Related Art
Various techniques have been used in the past to produce stereoscopic (three-dimensional) images for motion pictures or television. In general, these techniques involve two camera systems in which two different pictures are taken from slightly different camera angles and locations. The object is to simulate the manner in which depth is perceived by a pair of human eyes, which are themselves slightly offset from each other and thus view images at slightly different angles. The two camera images are superimposed and presented to the viewer simultaneously on a television or movie screen. The images are then separated in some fashion for the viewer so that one eye sees only one image, and the other eye sees only the other image. In this way an illusion of depth is created by simulating normal vision.
One technique which has been used to implement this approach is called the anaglyphic 3-D process, and has been employed in motion pictures and television. This technique uses color filters to separate the two images. The images are color coded, for example with red and green respectively, and the viewer is provided with glasses having different colored filters in front of each eye. Each filter rejects the image that is not intended for that eye, and transmits the image which is intended to be seen by that eye. A red color filter will pass only the red image, while a green color filter will pass only the green image. If the left eye image is presented as a green image and the right as a red image, and a green filter is placed in front of the left eye and a red filter in front of the right eye, the proper images will be directed to the proper eye and a 3-D image will be perceived by the viewer. An example of the anaglyphic process is disclosed in U.S. Pat. No. 3,697,679, entitled "Stereoscopic Television System", by the present inventor Terry D. Beard together with Eric R. Garen. A major shortcoming of the anaglyphic method is that the color filters interfere with the presentation of a high quality full color image. Color filters which fully reject the undesired image are difficult to make, with the result that the 3-D effect is imparired. This process is also difficult to use successfully in television because of the limited bandwidth transmission of color information in commercial broadcasts. The result of this limited bandwidth transmission is either ghost image interference or low resolution images.
Another 3-D process used in motion pictures is the so-called "Polaroid" process, in which the left and right eye images are separated by the use of polarizing light filters. The left eye image is projected onto the screen through a polarizing filter rotated 45.degree. to the left of vertical, while the right eye image is projected onto the screen through a polarizing filter rotated 45.degree. to the right of vertical. In this way the polarization of the two images are at right angles, and similarly polarized filters placed in front of each of the viewer's eyes will cause the proper image to be transmitted to each eye. This method is not adapted for 3-D television, and its use for motion pictures requires a special non-depolarizing projection screen.
Another technique which has been used to produce 3-D images on television involves the sequential presentation of left and right eye images to the viewer, together with the use of synchronized electro-optical glasses to switch on the filter in front of each eye when its image is being presented. This process is complicated and expensive, and requires special broadcasting and receiving equipment and electro-optical glasses.
A new technique for achieving 3-D television with the use of only one camera, and one image on the television screen, is described in U.S. Pat. No. 4,705,371 to the present inventor. This technique produces a noticeable 3-D effect by combining a particular type of viewer glasses with a specific filming technique. A moving picture of a scene is recorded such that a relative lateral movement is created between the scene and the recording mechanism. The lateral movement can result from movement of the objects themselves, or by moving the camera in various ways. The recorded scene is then viewed through a pair of glasses in which one lens has a greater optical density than the other lens, with the darker lens having a substantially higher transmissivity in the blue region than in the green or yellow regions. The optical density of the darker lens may also be reduced in the red region.
Since this last technique avoids the double images inherent in other 3-D television approaches, it has the distinct advantage of presenting a picture which appears to be perfectly clear and natural to an audience which does not have viewer glasses, and yet has a noticeable 3-D effect when the glasses are warn. However, the requirement for a substantial difference in neutral density has been found to be somewhat of a distraction for the viewer. The best 3-D effects occur with a neutral density difference between the two lenses in the order of 1.3 or more. With this large a differential, the reduced amount of light reaching the darkened eye is quite noticeable compared to the lighter lens, giving rise to a "dead eye" effect for that eye when objects other than the television screen are viewed. This can reduce the overall enjoyment of the 3-D viewing experience.
U.S. Pat. No. 4,705,371 proposed a number of modifications to the viewer glasses to reduce the "dead eye" effect. These included darkening the peripheral field of the lighter density lens while lightening the peripheral field of the darker density lens, or providing the light lens in the form of a light vertical strip with darker vertical strips on either side, and the dark lens as a dark vertical strip with light vertical strips on either side. The purpose of both approaches was to concentrate the neutral density differential in the center portion of the lenses, where the viewer generally concentrates his gaze. However, neither approach is very effective, and they give an odd appearance to the glasses while substantially increasing the complexity and expense of manufacture.